The subterranean termites found in scattered, localized areas around Iowa are routinely found in wood chip mulch and other wood products on or in the soil (lumber scraps, boards, firewood, pallets, etc.). Does this mean, as some pest control advertisements claim, that mulch attracts termites to your home or that the mulch somehow causes termites? The answer to both questions is, "no."
Landscape mulches contribute to a stable moist environment that is good for our trees and shrubs, and unfortunately, also good for termites and other insects. Termites in Iowa live underground in large, social colonies. Worker termites come to the soil surface (or higher) to feed on wood and other cellulose materials and carry it back to share with other colony members. Termites constantly explore for food by excavating a network of random, pencil-sized tunnels through the soil in the area surrounding their nest. Termites may tunnel for distances of up to 300 feet from their nest site. The presence of moisture favors termite exploration, tunneling and feeding. Therefore, any landscape mulch may improve conditions for termite colonies, whether the termites consume the mulch or not.
This does not mean you should avoid use of mulch, nor does it endorse one type of mulch as preferable over another. The same conclusion was recently reported from research at the Structural IPM Program at the University of Maryland. They studied the impact of landscape mulches on termite foraging activity in the laboratory and in the field. Termites that fed on a steady diet of either eucalyptus, hardwood or pine bark mulch suffered significantly lower survivorship than did termites fed the standard laboratory control diet of white birch. This result suggests that although we routinely discover termites in wood chip mulch, it is unlikely that they feed heavily on organic wood-based mulches.
In the field, termites were detected with equal frequency beneath mulches of eucalyptus, hardwood, pine bark and pea gravel and bare, uncovered soil. Sustained activity over time was significantly higher beneath gravel mulch. The hospitable conditions beneath mulch likely accounted for the termite foraging activity. However, there is no evidence that the moist conditions attract termite foragers from the surrounding landscape. Rather, when the termites wander into a suitable habitat they are more likely to remain and feed in that area.
Keep mulch several inches away from the house foundation. Never allow mulch to cover windowsills or to contact house siding. Watch wood chip mulch for signs of activity if termites are present in your area. If you suspect termite activity contact several professional termite control services for inspections and estimates. Termite treatment is best left to professionals experienced in the various methods of termite control. Take your time. Do not be rushed or pressured into a hasty decision. Termites work slowly and your house will not be ruined overnight. Deal with reliable firms and get several inspections, opinions and estimates.
This article originally appeared in the May 4, 2001 issue, p. 48.